1. Field of the Invention
The present invention relates to an impact tool which performs a predetermined operation on a workpiece by striking movement of a tool bit in its axial direction.
2. Description of the Related Art
Japanese laid-open patent publication No. 2008-73836 discloses a hammer drill as an example of an impact tool in which a striking mechanism part is driven via a swinging member which swings in the axial direction of a tool bit by the rotating output of a motor and the striking mechanism part linearly drives (strikes) a tool bit. The known hammer drill includes a counter weight that reduces vibration caused when the tool bit is driven. In the known hammer drill, the counter weight is disposed between an outer housing for forming an outer shell of the hammer drill and an inner housing for holding the striking mechanism part within the outer housing. Specifically, the counter weight is disposed outside the inner housing and configured to be moved in the axial direction of the tool bit by receiving power from the swinging member and thereby reduce vibration.
In this construction in which the counter weight is disposed outside the inner housing, however, it is necessary to provide clearances between the counter weight and the inner housing and between the counter weight and the outer housing in order to avoid interference in a direction transverse to the axial direction of the tool bit. This is an impediment to size reduction of the tool body.